diff --git a/config.mk b/config.mk
index aeabd6b..c6ae91d 100644
--- a/config.mk
+++ b/config.mk
@@ -1,17 +1,17 @@
 # st version
 VERSION = 0.8.2
 
-OS = $(shell uname)
+OS := $(shell uname)
 
 # paths
-ifeq $(OS) NetBSD
+ifeq ($(OS),NetBSD)
 PREFIX = $(HOME)
 else
 PREFIX = $(HOME)/.local
 endif
 MANPREFIX = $(PREFIX)/share/man
 
-ifeq $(OS) NetBSD
+ifeq ($(OS),NetBSD)
 X11INC = /usr/X11R7/include
 X11LIB = /usr/X11R7/lib
 else
@@ -29,13 +29,13 @@ LIBS = -L$(X11LIB) -lm -lrt -lX11 -lutil -lXft -lXrender \
        `$(PKG_CONFIG) --libs fontconfig` \
        `$(PKG_CONFIG) --libs freetype2`
 
-ifeq $(OS) NetBSD
+ifeq ($(OS),NetBSD)
 LIBS = $(LIBS) -Wl,-rpath,$(X11LIB)
 endif
 
 # flags
 STCPPFLAGS = -DVERSION=\"$(VERSION)\" -D_XOPEN_SOURCE=600
-ifeq $(OS) NetBSD
+ifeq ($(OS),NetBSD)
 STCPPFLAGS = $(STCPPFLAGS) -D_BSD_SOURCE
 endif
 STCFLAGS = $(INCS) $(STCPPFLAGS) $(CPPFLAGS) $(CFLAGS) -mtune=native -march=native -O3 -pipe -fstack-protector-strong -fno-plt